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Tuesday, July 22, 2014

It is time to consider applying fungicide

Posted Wednesday, July 13, 2011, at 5:52 PM

The corn crop is in general looking good. The warm weather, sun and rainfall have given it a chance to take off.

A lot of the corn has either tasselled or is tasselling. The corn is now at its most critical yield determining part of the season.

Crop color is good to outstanding in most fields with limited Nitrogen (N) deficiencies showing in a few fields.

The dark green color means that photosynthetic rates are high, and as leaf area and light interception approach their maximum, the crop is producing sugars at maximum rates. This is exactly what the crop needs to do as it enters the pollination stages. We need to remember that the effect of good conditions now can be overcome if it turns hot and dry later in July.

Signs of dropping photosynthetic rates are almost always visible as leaf symptoms. These would include loss of dark green color, curling up die to lack of adequate water, disease damage to leaf area, or loss of leaf area from hail or insects.

The appearance of a corn crop is an excellent diagnostic tool for nitrogen. If corn is yellow-green or light green, it is most likely N-deficient. Applying nitrogen this late in the season is later than ideal, but could help manage a serious nitrogen deficiency. The highest demand for nitrogen is at tasselling.

It is close to the last call for applying rescue nitrogen to corn fields, according to Peter Scharf, MU Extension soil scientist. According to Scharf, there is still time to add nitrogen to increase yields. Nitrogen can be added until July 15 in northern Missouri to increase yields. Scharf has seen yield increase with nitrogen fertilizer at tasseling time. Scharf indicates that he would keep applying nitrogen until two weeks after tasseling if the corn needed it.

Another consideration for this time of year is the application of fungicides to the corn crop.

The plant diagnostic lab has received few samples of leaf diseases on corn so far this year. What symptoms that were present early in the season have now become hard to find with the rapid growth of the corn plant.

In general, corn foliage diseases that appear later in the season (especially the longer after pollination) that the foliage disease becomes established, the lower direct yield losses will be. In deciding whether or not to apply a foliar fungicide, it is important to consider the yield potential of each field.

If fields are uneven and struggling because of wet conditions, foliar fungicides are less likely to give significant increases in yield.

If nitrogen loss is a problem, it may be more beneficial to correct the nitrogen deficiency than apply a fungicide.

Susceptible hybrids may give better yield increase than disease hybrids. Later planted fields which will have plants at earlier growth stages later in the season may also benefit more from fungicide applications.

With the wide range in planting dates and plant vigor across the state, individual fields need to be monitored for stand, vigor, yield potential, nitrogen loss, weed escapes, and presence and severity of disease before deciding to apply a foliar fungicide.



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As our local University of Missouri Agronomy Extension Specialist, Crook has been writing a column for the print edition Agriculture page for the past three years and we will now be sharing it on our web version. Crook has a bachelor and masters degree in agronomy from University of Missouri and received his doctorate in Agronomy from Kansas State University. He was in soybean variety development research for 22 years for various seed companies and has been Saline County's agronomy specialist for 10 years.
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